RE: [PATCH v3 2/2] mmc: core: Call mmc_poweroff_nofity() if pm_suspend_via_firmware()

Hi Ulf, Geert,

From: Geert Uytterhoeven, Sent: Wednesday, June 24, 2020 8:13 PM

Hi Ulf,

On Wed, Jun 24, 2020 at 12:06 PM Ulf Hansson [off-list ref] wrote:

quoted

On Mon, 22 Jun 2020 at 04:25, Yoshihiro Shimoda
[off-list ref] wrote:

quoted

If pm_suspend_via_firmware() returns true, the system will be able
to cut both vcc and vccq in the suspend. So, call
mmc_poweroff_nofity() if pm_suspend_via_firmware() returns true.

Note that we should not update the MMC_CAP2_FULL_PWR_CYCLE caps
because the mmc_select_voltage() checks the caps when attaches
a mmc/sd.

quoted

quoted

--- a/drivers/mmc/core/mmc.c
+++ b/drivers/mmc/core/mmc.c

@@ -2038,7 +2039,8 @@ static int _mmc_suspend(struct mmc_host *host, bool is_suspend)
                goto out;

        if (mmc_can_poweroff_notify(host->card) &&
-               ((host->caps2 & MMC_CAP2_FULL_PWR_CYCLE) || !is_suspend))
+           ((host->caps2 & MMC_CAP2_FULL_PWR_CYCLE) || !is_suspend ||
+            pm_suspend_via_firmware()))

Sorry, but this doesn't work.

Even if PSCI is a generic FW interface, it doesn't mean that all PSCI
implementations will cut the vcc and vccq for the MMC card at system
suspend.

Indeed, there's nothing guaranteed here.  Nor documented how it should
behave.  Basically the firmware is free to power off the SoC. Or not do that.
"If firmware is involved, all odds are off".

I thought we could be guaranteed. But, I understood we could not be guaranteed...

quoted

Instead, you need to decide this based on some specific DT property.
Perhaps in conjunction with using pm_suspend_via_firmware().

Last time I was involved in a discussion about this, the PSCI people
didn't want to add any properties describing particular PSCI behavior...
"If firmware is involved, all odds are off".

So the only safe thing to do is to expect the worst, and prepare for it...

A headache point is an eMMC device consumes much power if that the system
doesn't cut the vcc and vccq and doesn’t enter the sleep mode.
In other words, in power consumption point of view, this patch will
cause a regression in such a case...

By the way, about adding specific DT property, the regulator can have
regulator-off-in-suspend property in regulator-state-mem subnode.
For now, we doesn't seem to get the property from a regulator consumer though.
So, I'll try to add an API of regulator for it.

Best regards,
Yoshihiro Shimoda

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds

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